<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>引入方式</title>


</head>
<body>
<button id="bun">单击</button>

<!--<script>
    document.getElementById("bun").onclick=function () {
        alert("内部")
    }
</script>-->

<script src="js.js"></script>

</body>
</html>